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Rev. Inst. Med. trop. S. Paulo
45(4):185-191, July-August, 2003



                                                   Dahir Ramos de ANDRADE & Dahir Ramos de ANDRADE JÚNIOR


             The knowledge about typhoid fever pathogenesis is growing in the last years, mainly about the cellular and molecular phenomena
         that are responsible by clinical manifestations of this disease. In this article are discussed several recent discoveries, as follows: a)
         Bacterial type III protein secretion system; b) The five virulence genes of Salmonella spp. that encoding Sips (Salmonella invasion
         protein) A, B, C, D and E, which are capable of induce apoptosis in macrophages; c) The function of Toll R2 and Toll R4 receptors
         present in the macrophage surface (discovered in the Drosophila). The Toll family receptors are critical in the signalizing mediated by
         LPS in macrophages in association with LBP and CD14; d) The lines of immune defense between intestinal lumen and internal
         organs; e) The fundamental role of the endothelial cells in the inflammatory deviation from bloodstream into infected tissues by
         bacteria. In addition to above subjects, the authors comment the correlation between the clinical features of typhoid fever and the
         cellular and molecular phenomena of this disease, as well as the therapeutic consequences of this knowledge.

         KEYWORDS: Typhoid Fever; Salmonella enterica serovar Typhi; Cellular Microbiology; Bacteria-Cell interaction.

    Classically, typhoid fever is considered a disease of multiple stages:                  The knowledge about typhoid fever raises some doubts. The use of
1) the first week is characterized by progressive elevation of the                      microbicide therapeutic should be evaluated in relation to the risks of
temperature, followed by bacteremia; 2) the second week comes with                      disease worsening because of elevation of the lipopolysaccharide (LPS)
rose spots in the skin, abdominal pain, and splenomegaly; 3) the third                  molecules. These molecules are called as LPS/endotoxin, and they are
week marks a more intensive intestinal inflammatory process, particularly               responsible for the mononuclear cell activation that release cytokines as
in the Peyer’s patches, and complications may develop as digestive                      TNF-alpha, IL-1, IL-6, IFN-gamma, etc.
bleeding and intestinal perforation. The patients may have clinical
recovery afterwards. However, some patients may die after a progressive                     LPS is considered a powerful agent for the inflammatory cells
clinical worsening not responsive to the treatment with antibiotics against             activation, and it acts through CD14, Toll R2 and Toll R4 receptors.
Salmonella enterica subsp. enterica serovar Typhi (S.Typhi).                            Through them, LPS transmits signals to intracellular protein chain known
                                                                                        as p21 activated kinase (PAK) studied in Salmonella enterica serovar
     The knowledge about typhoid fever pathogenesis has grown in the                    Typhimurium (S.Typhimurium) 10. Other proteins activated by S.
last years, mainly about the cellular and molecular phenomena that are                  Typhimurium are the Rho-GTPases that are capable to stimulate the
responsible by clinical manifestations of this disease. In this article are             membrane “ruffling” (the rearrangement of cellular membrane), through
discussed some recent discoveries about Salmonella spp. as follows: a)                  which Salmonella spp. entry into the cells. At this moment, the
bacterial type III protein secretion system (TTSS); b) the five virulence               rearrangement of actin cytoskeleton and the nuclear responses also
genes (A, B, C, D and E) of Salmonella spp. that encoding Sips                          happens.
(Salmonella Invasion Proteins); c) Toll R2 and Toll R4 receptors present
in the macrophage surface, that are critical in the signalizing mediated                    The contact of cytosol with proteins secreted by invasive bacteria
by LPS in macrophages; d) the lines of immune defense between intestinal                (S.Typhi, S.Typhimurium, S. Cholerae-suis, etc.) is made through protein
lumen and internal organs; e) the fundamental role of the endothelial                   channels named type III secretion system (TTSS) that translocate bacterial
cells in the inflammatory deviation from bloodstream into infected tissues              proteins inside of the cells. The genetic acquisition of TTSS was a major
by bacteria. With the new discoveries about typhoid fever pathogenesis,                 evolutionary leap for gram-negative bacterial pathogens. TTSS allow
we consider this disease as an authentic cellular microbiological model                 animal and plant pathogens to inject their own proteins, termed effectors,
of study.                                                                               directly into host cells and that modulate specific host cellular functions27.

Laboratório de Investigação Médica – LIM 54, School of Medicine, University of São Paulo, São Paulo, SP, Brazil.
Correspondence to: Dr. Dahir Ramos de Andrade, Av. Paes de Barros 701, ap. 101, Mooca, 03115-020 São Paulo, SP, Brazil. Phone: 55.11.66051531. Fax: 55.11.30830827. Email:
ANDRADE, D.R. & ANDRADE JÚNIOR, D.R. - Typhoid fever as cellular microbiological model. Rev. Inst. Med. trop. S. Paulo, 45(4): 185-191, 2003.

These ‘molecular syringes’ and their secreted effectors are essential                         3) Main host immune defense: The main host defense against
virulence determinants. The protein Sop E is substratum of this secretion                Salmonella spp. occurs through the neutrophils at first, followed by
system, and it stimulates the cytoskeleton reorganization followed by                    mononuclear cells. These inflammatory cells produce cytokines as Tumor
the JNK protein chain activation, which is dependent of Rac-1 and CDC                    Necrosis Factor alpha (TNF-alpha), Interferon-gamma (IFN-gamma),
42 19. MAP kinases’s role in the nuclear responses and cytokines                         IL-1, IL-2, IL-6 and IL-8. The Kupffer cell is the main TNF-alpha
production induced by inflammatory cells and by cultured intestinal cells                producer in the liver. Several studies have shown that epithelial cells
were discussed in another study22. These recent publications about                       play a central role in coordinate the intestinal inflammatory response to
mechanisms of Salmonella spp. action highlightes the knowledge of the                    intestinal pathogens. The interaction of Salmonella spp. with epithelial
evolution of molecular and cellular phenomena in the human typhoid                       cells leads to the generation of a great number of biochemical signals by
fever. These phenomena are the base of disease’s symptoms and clinical                   these cells. These include the basolateral release of chemokines (including
manifestations.                                                                          IL-8) and apical secretion of “pathogen - elicited epithelial
                                                                                         chemoattractant” (PEEC)13,33. These substances are partially responsible
                 TYPHOID FEVER PATHOGENESIS                                              for guide the recruitment and traffic of PMNs across CEIs. In recent
                                                                                         study was showed that S. Typhimurium induces IL-8 secretion by
     1) Intestinal mucosal Immunity (first line of defense): The                         intestinal epithelia through increase in intracellular calcium. This
infectious dose of S.Typhi in volunteers varies between 1000 and 1                       phenomenon was NF-kappaB dependent18. A functional TTSS is required
million organisms25. This bacterium must survive the gastric acid barrier                for the induction of PMN transmigration. Furthermore, protein synthesis
to reach the small intestine, and a low gastric pH is an important defense               in both bacteria and epithelial cells is also required for this activity.
mechanism. In the small intestine, S. Typhi moves across the intestinal                  Invasion of Salmonella spp. into epithelial cells is insufficient for
epithelial cell (CEI) and reach the M cells, thus penetrating in the Peyer’s             transepithelial signaling to PMNs, and PMN migration occurs even when
patches. The M cells, specialized epithelial cells overlying Peyer’s                     Salmonella spp. invasion is blocked17.
patches, are probably originated from CEI and small pockets in the
mucosal surface characterize them. After contact with M cells, the                           The “inflammatory deviation” that happens when blood leukocyte
infectious agents are rapidly internalized and they reach firstly a group                migrates across endothelial cells into hepatic and spleen tissues is another
of antigen-presenting cells (APCs), being partially phagocytized and                     important event. This phenomenon occurs through the action of adhesion
neutralized. Some bacteria escape of this barrier, and they reach the well-              molecules named integrins (chain αβ) in inflammatory cells and selectins
developed lymphoid follicles (Peyer’s patches), formed mainly by                         in endothelial cells (E and P). Afterward, selectins are substituted by
mononuclear cells as T lymphocytes, as well as dendritic cells. Dendritic                ICAMs and VCAMs proteins (whose partner in inflammatory cells is
cells present the bacterial antigens and they provoke T and B lymphocytes                VLA4 or α4β1 integrin). The inflammatory microenvironment is
activation.                                                                              completed by chemokines that are capable to stimulate leukocyte motility
                                                                                         (chemokinesis) and directed movement (chemotaxis) of neutrophils and
     2) Dissemination from intestinal mucosa’s lamina propria:                           mononuclear cells. Chemokines bind to CC and CXC receptors in the
Starting from lamina propria, T and B lymphocytes activated come out                     surface of inflammatory cells. The chemokines help the blood leukocytes
for the lymphatic nodules. They will reach the mesenteric veins through                  migration straight for host cells infected by bacteria.
lamina propria blood vessels, and then they arrive to liver and spleen. In
these organs, the bacteria are destroyed mainly after phagocytosis by                        TNF-alpha is a cytokine produced by macrophages and other
macrophage system. However, Salmonella spp. organisms are able to                        mononuclear cells, and it has the greater antibacterial agent against
survive and multiply within the mononuclear phagocytic cells26.                          Salmonella spp. TNF-alpha in association with IFN-gamma, IL-2 and
                                                                                         other cytokines, will be responsible for the neutralization of this invasive
    At a critical point determined by the number of bacteria, the bacterial              bacteria, besides the macrophage phagocytosis.
virulence and the host immune response, bacteria are released from their
sequestered intracellular habitat into the bloodstream. This bacteremic                      4) Apoptosis and the human Toll receptor activated in typhoid
phase of disease is characterized by widely dissemination of the                         fever: Typhoid fever disease is an important example of severe sepsis,
organisms. The most common sites of secondary infection are the liver,                   because it presents enormous amount of cellular death (necroapoptosis)
spleen, bone marrow, gallbladder and Peyer’s patches in the terminal                     besides severe toxemia32. In this way, there are newest discoveries about
ileum. In the liver, S. Typhi provokes Kupffer cells activation. Kupffer                 the Toll R2 and Toll R4 receptors studied in Drosophila.
cells have high microbicide power, and they neutralize the bacteria with
oxidative enzymes (via oxygen free radicals, nitric oxide, etc.), as well                     The innate immune system uses Toll family receptors to sign microbes
as enzymes active in acid pH. These cells constitute the most effective                  presence and to start host defense. Bacterial lipoprotein (BLP) expressed
barrier to invasive bacteria as S. Typhi and S. Typhimurium. The survivor                in all bacteria species are potent activators of “Toll-like receptor 2” (Toll
bacteria reach and invade hepatocytes, and they will cause high cellular                 R2). The innate immune system includes macrophages and natural killer
death rate, mainly apoptosis3. The apoptosis occurs through activated                    (NK) cells that act directly on pathogens through cytokines and other
kinases that phosphorylase protein responsible for signs transmission to                 stimulatory molecules, which activate the adaptive immune responses
the nucleus. In our laboratory, we could verify that the rat hepatocytes                 (cellular and molecular) through T and B lymphocytes35. The innate
produce TNF-alpha in a time-dependent and progressive form when                          immune system (first line of defense) identifies the pathogens by standard
invaded by S. Typhimurium4,5. This phenomenon is very important, since                   recognition receptors, which attach to microbial macromolecules. In this
the TNF-alpha is capable to amplify the local inflammatory response                      way, macrophage mannose receptors attach to structures with repeats of
and to induce the hepatocyte death by apoptosis.                                         polimannose. CD14 receptor, described some time ago, was considered

ANDRADE, D.R. & ANDRADE JÚNIOR, D.R. - Typhoid fever as cellular microbiological model. Rev. Inst. Med. trop. S. Paulo, 45(4): 185-191, 2003.

as fundamental to recognize LPS/endotoxin in the surface of gram-                        receptors and FADD protein (Fan-associated death domain). FADD
negative bacteria like Salmonella spp. before the discovery of the Toll                  through death domain contacts homologous area in caspase-8 prodomain,
R2 receptor. The difference between CD14 and Toll R2 is that the former                  that cleaves effective caspases 3 and 7 and activate the apoptosis
are a “GPI” (glycosyl-phosphatidylinositol) receptor, that does not cross                program1,2. This final connection, bind TLR2 to cell apoptosis machine2.
the cellular membrane, and does not transmit signs for cytoplasm or
activate protein chains of macrophages23,35. In contrast, Toll R2 molecule                   5) Protein secretion mechanisms and other virulence mechanisms
cross the cellular membrane, and transmits signs for the intracellular                   of Salmonella: Bacteria as Salmonella spp.6,38 have type III secretion
protein chains. The activation of these protein pathways will spread to                  system that to permit for they inject bacterial proteins in several host
transcriptional factor NF-kB that will migrate to cellular nucleus starting              cells, such as: CEIs, hepatocytes, endothelial cells and inflammatory
from cytoplasm. NF-kB recognizes and liberates genes encoding the                        cells (neutrophils, monocytes-macrophages, T and B lymphocytes etc.)20.
adhesion molecules, TNF- alpha and another Th1 cytokines (IFN-gamma,
IL-2, etc.). The patients with failure of immune response to combat the                      Recent progresses in cellular microbiology15 have highlight the role
infection by macrophage activation may evolve to septic shock37.                         of type III secretion system as a protein secretion system highly
                                                                                         specialized found in gram-negative pathogens. As mentioned above, this
    The pathogens have molecular antigens that are recognized by                         system transfers proteins from bacterial cytoplasm into the host cell
receptors as: LPS of gram-negative bacteria, glycolipid of mycobacteria,                 cytoplasm, with purpose of interfere in the host cellular function.
lipoteichoic acid of Gram-positive bacteria, mannans of yeast, RNAs of
virus and others28,34.                                                                       TTSS includes more than 20 proteins, and it is considered the most
                                                                                         complex bacterial protein secretion system associated with the pathogen
    Two LPS binding protein, BPI (bactericide permeability increasing                    virulence. The structural components of TTSS can be divided in two
protein) and LBP (lipopolysaccharide binding protein) have fundamental                   groups. One group consists of outer membrane proteins (including one
importance, because their connection with LPS results in distinct effects.               similar to secretin family), and the other group has several integral
BPI (55 kD) has an antimicrobial role and it is present in neutrophils                   membrane proteins (similar to flagellar export apparatus). Supramolecular
with selective toxicity against gram-negative bacteria. This protein is                  structure associated with TTSS of S. Typhimurium was visualized by
more effective when acts on neutrophils phagocytosis in synergism with                   electronic microscopy. This structure consists of a needle complex, spans
defensins (intestinal mucosa’s antimicrobial). LBP increases the                         both the inner and outer membranes of bacterial envelope. The needle
sensitivity to LPS allowing that effector cells are activated by                         complex has a long hollow structure about 120 nm long and it is
subpicomolar LPS concentrations. LBP recognizes Lipid A, that is the                     composed of two domains. The first is a needlelike portion projecting
half biologically active of the endotoxin molecule42,43. LBP also carry                  outward from the bacteria surface and the second portion has a cylindrical
out an important role in the bacterial clearance of peripheral blood through             base that anchors the structure to inner and outer membranes.
                                                                                             The biochemical analysis revealed that the needle complex is
    Recently, some studies indicate that Toll family receptors (TLRs)                    composed of three proteins: InvG (a member of secretin family), PrgH
are critical in the signalizing mediated by LPS, in association with LBP                 and PrgK (lipoproteins). TTSS is an ATP – dependent system. S.
and CD1423. The identification of a Toll human receptor homologous                       Typhimurium injects in host cells a set of effectors proteins inducing
(well known in Drosophila) named as hTLR4 (Toll-like human receptor                      actin cytoskeleton rearrangements, membrane ruffling and macro-
4), was a great discovery in knowledge on the complex binding receptor                   pinocytosis that finish in bacterial invasion. The effectors proteins include
with LPS34.                                                                              an exchange factor for Rho GTPases (Sop E), an inositol phosphate
                                                                                         phosphatase (Sop B), and an actin-binding protein (Sip A)44. Sop E acts
     Nowadays six members of the “TLRs” family are known, and two                        as an exchange factor for a subset of Rho GTPases, including CDC42
of them TLR2 and TLR4 were associated with LPS signalizing. However,                     and Rac. SopE and possibly other Sops induce enterocyte membrane
only TLR4 has been considered a LPS signalizing in humans8,21,41.                        ruffling promoting bacterial cellular invasion. Sop B modulates the actin
                                                                                         cytoskeleton through its inositol phosphate phosphatase activity, which
    The hTLR4 protein has a repetitive sequence rich in leucine in its                   generates a broad range of inositol phospholipids and inositol phosphates.
extracellular domain that interacts with complex CD14 - LPS. TLR4                        The intracellular SopB protein affects inositol phosphate signalling
and other TLRs have a TIR cytoplasmic receptor (Toll-IL-1 receptor)1,2,39                events. One such event is a transient increase in concentration of Ins
in homologous domain to IL-1 receptor (IL-1R). This domain                               [1,4,5,6] P4, which can antagonize the closure of chloride channels,
communicates with an adapting protein My D88 (myeloid differentiation                    influencing net electrolyte transport and fluid secretion. Sip A inhibits
factor 88) that interacts with TLR4 starting cell signalizing as follows:                the F-actin depolymerization after its binding to actin. Pathogen-induced
IL-1R associated kinase (IRAK-1), TNF-alpha receptor (TNFR)                              remodeling of the host cell actin drives internalization of invasive
associated factor 6 (Traf-6) and NF-kB inducing kinase (NIK). The                        Salmonella by non-phagocytic CEIs.
kinases IRAK-1 and NIK phosphorylase inactive complex in the
cytoplasm named IkBs (IKKα and IKKβ), causing its degradation                                Two Salmonella actin-binding proteins are involved in bacterial
through ubiquination-proteasome. This reaction releases the NF-kB/REL                    internalization: SipC that is essential for the internalization process, and
dimer, and NF-kB migrates for nucleus when immunomodulatory genes                        SipA that enhances its efficiency44.
will be activated. In consequence, there is synthesis of cytokines, adhesion
molecules (ICAMs), stress proteins (HSPs), and activation of inhibitor                      S. Typhi and other Salmonella serovars have two phenotypes
of apoptosis genes (IAPs). TLR2 transmits a proapoptotic sign via death                  associated with TTSS: one is involved in bacterial invasion to

ANDRADE, D.R. & ANDRADE JÚNIOR, D.R. - Typhoid fever as cellular microbiological model. Rev. Inst. Med. trop. S. Paulo, 45(4): 185-191, 2003.

nonphagocytic cells, as well as induction of apoptosis in macrophages                        The potent inflammatory reaction against Salmonella spp. has the
through Sip B21; the other is required for bacterial survival inside                     inconvenience of to provoke the host cells death, as well as the apoptosis
macrophages and for systemic infection.                                                  of both inflammatory and epithelial cells. This phenomena result in the
                                                                                         appearance of several clinical signs as fever, jaundice (due to hepatocytes
    Nowadays, a new group of virulence genes has been identified in                      death and cholangiocytes activation), and increase of enzymes AST, ALT,
Salmonella, named Sips (Salmonella invasion proteins) containing five                    γ-glutamyltranspeptidase, alkaline phosphatase, etc. The amino-
genes: Sip A, Sip B, Sip C, Sip D and Sip E. Sip B gene encodes Sip B                    transferases rise in moderate levels (100 to 300 UI/l), and γ-
protein that is involved in proteins translocation via TTSS, and it has                  glutamyltranspeptidase and alkaline phosphatase (markers of activated
potential to induce apoptosis in macrophages through caspase-1                           cholangiocytes) may reach 50 to 300 UI/l. These latter two enzymes are
activation. This fact was showed through Sip B injection in macrophages,                 situated in the biliary cell membrane.
which caused apoptosis by caspase-1 activation 36. In Salmonella,
however, Sip B role inducing apoptosis and concomitant release of IL-1                       The increase of cytokines in the peripheral blood will cause fever
beta (proinflammatory cytokine) is unclear (in contrast to Shigella).                    after incubation period of 5 to 21 days. Initially the fever is low grade,
                                                                                         but it rises progressively, and by the second week it is often high and
    Another peculiar aspect of Salmonella was showed by ECKMANN                          sustained (39 °C to 40 °C). The fever occurs in more than 80% of patients
et al.14. In this study, the CEIs invaded by Salmonella increased the                    in both sexes31, with men predominance. The classic disease description
cytokines mRNAs expression as G-CSF, IL-8, MIP-2α, and transcription                     includes bacteremia and fever during the first week, as well as nonspecific
factors as IRF-1 and NF-kB, as well as HLA class I. These discoveries                    symptoms as chills, headache, anorexia, sore throat, myalgia, psychosis
allow understanding better the bacteria – cell interaction.                              and mental confusion in 5 to 10% (typhoid state). A coated tongue,
                                                                                         tender abdomen, hepatomegaly, and splenomegaly are common. In the
     Recently, HOOPER & GORDON24 showed that serovars of avirulent                       second week, a few rose spots, blanching erythematous maculopapular
Salmonella spp. are capable to inhibit cytokines production by CEIs.                     lesions, approximately 2 to 4 mm in diameter appear in 5 to 30 percent
This phenomenon involves IkB that blocks the NF-kB migration to                          of cases. They usually occur on the abdomen and chest and more rarely
nucleus. The avirulent Salmonella inhibited the IkB ubiquination and                     on the back, arms, and legs. A relative bradycardia in relation to fever,
its degradation by proteasome 26S. Thus, genes transcription managed                     intestinal constipation, and diarrhea in smaller number of patients (mainly
by NF-kB was blocked. These genes encode proinflammatory mediators                       in young children and adults with HIV infection) may occur. This classic
as cytokines, chemokines and adhesion molecules.                                         pattern of typhoid fever has been modified by earlier diagnosis and more
                                                                                         effective treatment. In spite of these advances, some patients still may
    The knowledge of bacterial pathogenesis was increased by virulence                   present the clinical manifestations of first and second weeks. In the cases
genes discovery, which are acquired by pathogens and introduced in                       without treatment or correct diagnosis, the typhoid fever prolongs to
bacterial DNA. Nowadays, these genes are known as “pathogenicity                         third week. In this period, the inflammatory lesions are intense in Peyer’s
islands” (PAIs) involving a great genetic area with more than 100                        patches and intestinal lamina propria (with abundant monocytes,
kilobases (kb). Five PAIs have been identified in the Salmonella species.                macrophages and lymphocytes). There is lymphoid hyperplasia in the
Two of these PAIs, Salmonella pathogenicity island (SPI)-1 and SPI-2,                    ileocecal area followed by ulceration and necrosis (cellular death), with
encode TTSS, which are essential virulence determinants. SPI-1 and                       subsequent gastrointestinal bleeding or intestinal perforation.
SPI-2 are expressed under distinct environmental conditions: SPI-1 is                    Complications occur in 10 to 15 percent of patients and they can evolve
induced after initial contact with the host cell, whereas SPI-2 is induced               to death, in general after the third week of disease. Symptoms as anorexia,
intracellular. In spite of bacterial diversification, gene transfer capacity             weigh loss, intense weakness, mental confusion, and others, may occur
to become a microorganism of success is variable. In Salmonella are                      in typhoid fever especially when there is a delay in the diagnosis and
necessary five pathogenicity islands for disease evolution40. In contrast,               treatment.
in Escherichia coli one pathogenicity island is enough to increase
bacterial virulence.                                                                          Relapse of disease occurs in 5 to 10 percent of patients, usually two
                                                                                         to three weeks after the fever resolution. The high fever and progressive
    6) Clinical manifestations of typhoid fever and their                                abdominal pain appear again. This phenomenon may be owing to
pathogenesis: S. Typhimurium and other serovars causes gastroenteritis                   secondary bacteremia from normal enteric flora due to Peyer’s patches
with intestinal acute inflammation of limited duration in people with                    inflammation. The fever declines in the 4th week of disease in 90% of
normal immune defense. S. Typhi is responsible for typhoid fever in                      survivors, without antibiotic therapy. However, weakness and weight
humans, a disease with high clinical toxicity and possible evolution to                  loss may persist during many months. Pyogenic meningitis, acute
death6,38.                                                                               cholangitis and mural endocarditis are rare manifestations of typhoid
                                                                                         fever. The immune response against S. Typhi has probably similar
    The symptoms and clinical signs in patients with typhoid fever are                   influence in all these clinical conditions.
related to cellular microbiological phenomena12. The bacterial invasion
of several host cells and the inflammatory response (neutrophils,                            The true “sepsis”, which constitutes the severe typhoid fever disease,
monocytes-macrophages, T and B lymphocytes) with high cytokines                          is caused by LPS/endotoxin molecules that are abundant in the surface
production are important elements causing the clinical manifestations.                   of Enterobacteriaceae as Salmonella spp., Escherichia coli, etc. These
Cytokines produced (IL-1, IL-6, TNF-alpha, Interferons - α, β and γ)                     molecules are capable to activate the macrophages, through cell surface
are also responsible for fever emergence, with four weeks length in the                  receptors known like CD14, Toll R2 and Toll R4 (in humans) as
typhoid fever without treatment.                                                         mentioned above. The inflammatory response of Th1-dominant type is

ANDRADE, D.R. & ANDRADE JÚNIOR, D.R. - Typhoid fever as cellular microbiological model. Rev. Inst. Med. trop. S. Paulo, 45(4): 185-191, 2003.

destructive for host cells and for bacteria. Th1 response attenuates                     respectively. In the convalescence, there was progressive decrease of
progressively, and this coincides with increase of Th2- immune response.                 cytokines in the disease recovery. Probably, the presence of cytokines
Th2 cells produce IL-4, IL-10, IL-13, TGF-β, that causes a powerful                      inhibitors were necessary to counterbalance the high values of
protecting effect in the host cells (hepatocytes, CEIs, inflammatory cells               proinflammatory cytokines. The same authors studied the influence of
etc.), through the partial inhibition of cytokines associated with Th1                   blood peripheral 14 kDa group II phospholipase A2 (PLA2) in 12 patients
cells. The predominance of Th1 immune response can be detected by                        with typhoid fever, after admission and after recovery30. On admission,
the immunohistochemistry technique with specific antibodies. Another                     PLA2 levels were high (1444 ± 1560 ng/ml), and decrease gradually to
available technique is bioassay or immunoassay that detect cytokines                     55 ± 48 ng/ml at 14th day. Patient with complicated typhoid fever had
(as IFN-gamma) in peripheral mononuclear cells by the flow cytometer                     significantly higher PLA2 levels on admission (2520 ± 48 ng/ml). The
or “ELISPOT”. The ELISPOT technique is of recent discovery and it is                     authors suggest that PLA2 may be a mediator of seriousness in prolonged
capable to evaluate cellular frequencies in a quantitative way, through                  inflammatory diseases such as typhoid fever30.
identification of cells producing IFN-gamma that characterize Th1
immune response.                                                                             The extensive knowledge of typhoid fever’s molecular and cellular
                                                                                         pathogenesis, allow to all of us better understanding of its clinical phases,
     The deficiency in inhibit the proinflammatory cytokines TNF-alpha,                  and more rational approach of the patient’s clinical manifestations. In
IFN-gamma, IL-2, etc., will result in cellular destruction predominance                  the future, we will be able to decrease the intensity of inflammatory
in relation to cellular protection. This phenomenon provokes serious                     phenomena, through therapeutic maneuvers intending to disable
tissue lesions, as intestinal perforation and hemorrhage. The patient’s                  inflammatory cells (with cytokines decrease), as well as to inhibit the
clinical condition is worse by these complications, and surgery or effective             cellular death (hepatocytes, inflammatory cells, etc.) related to Salmonella
hemostasia is necessary. At this moment, the patients have profound                      spp. invasion.
weakness (due to high inflammatory reaction), high fever, weight loss
and other clinical manifestations. The ability of clinicians and surgeons                    7) Therapeutic cconsequences of typhoid fever pathogenesis: The
to resolve these problems has been responsible for the patients’ survival.               recent concepts about typhoid fever pathogenesis described above may
                                                                                         influence the therapeutical approach of this disease. In this way, the
    The gastrointestinal bleeding should be attributed to endothelial cells              glucocorticoids should be used in association with antibiotics in the adults
activation through the increase of inflammatory cytokines and circulating                and children with severe typhoid fever characterized by high fever,
LPS/endotoxin, mainly in the intestines. This result in high rate of                     delirium, obtundation, coma or shock.
endothelial cell death, and erosion of a necrotic tissue through the enteric
vessel wall. The vessel basal membrane rich in collagen is exposed                           Recently, a study performed in Jakarta9 showed that patients with
allowing the adherence of activated platelets. In addition, endothelial                  severe typhoid fever treated with chloramphenicol and dexamethasone
cells with the participation of pro and anticoagulation systems also                     have lower mortality as compared to chloramphenicol group. The patients
activate the coagulation cascade. This microenvironment will be                          receiving dexamethasone had significant decrease of mortality from 56%
responsible for the bleeding and CEI death, ulcerated lesions and                        to 10%. In spite of the doubts about this study model, dexamethasone
intestinal (usually ileal) perforation.                                                  should be considered for typhoid fever treatment in cases with mental
                                                                                         alterations or shock. However, glucocorticoid administration should be
     B lymphocytes are found in the central area of lymphoid follicles,                  avoided besides 48 hours, because the increased risk of disease relapses11.
and migrate across vascular walls together with T lymphocytes. Some
lymphocytes are retained in the mesenteric lymph nodes, and they will                         Despite of the study mentioned above, the physicians should have
become plasma cells in the return to intestinal mucosa’s lamina propria.                 caution with the use of glucocorticoids associated with antibiotics in
At this moment, these cells are capable to produce IgG and IgM                           cases of severe typhoid fever, due to the recent knowledge about the
immunoglobulins, as well as secretory IgA that is considered the first                   mechanism of action of these antiinflammatory substances.
line of intestinal defense. The final molecular junction of dimeric IgA                  Glucocorticoids acts in macrophages and host cells (intestinal cells,
occurs within intestinal lamina propria. In this site, IgA receives a                    hepatocytes, etc.) through blockade of transcriptional factor NF-kB that
protecting component produced by CEIs and remains resistant to digestive                 is responsible for cytokines release as TNF-alpha, IL-1, IL-6, IL-8, IFN-
enzymes. Afterwards, IgA is secreted for intestinal lumen by paracellular                gamma and others. NF-kB migrates to the nucleus of infected cells, where
via, covering the mucosa surface. Together with other protectors elements                it activates its target genes responsible for cytokines synthesis. Usually,
of intestinal mucosa as intestinal flora, local antimicrobial, etc., the                 NF-kB is hold in inactive form by IkBα proteins in the glucocorticoids
secretory IgA constitutes the main element of the intestinal humoral                     presence, and it remains in the cytoplasm7. Some studies show that
defense.                                                                                 glucocorticoids increase transcription of IkBα gene, and IkBα
                                                                                         concentrations go up within the cell. Other studies show that the
    KEUTER et al.29 described the patterns of proinflammatory cytokines                  glucocorticoid receptor complex bind to NF-kB and blockade its binding
in 44 patients with typhoid fever, through ELISA or RIA. The circulating                 in DNA. TNF-alpha actuating through its cellular receptors TNFR-I or
cytokines levels in the acute phase of disease were as follows (± SD):                   TNFR-II is responsible for IkB phosphorylation and its degradation
IL-1β =
ANDRADE, D.R. & ANDRADE JÚNIOR, D.R. - Typhoid fever as cellular microbiological model. Rev. Inst. Med. trop. S. Paulo, 45(4): 185-191, 2003.

     Through the knowledge of molecular mechanisms of corticosteroid                           9. BUTLER, T.; ISLAM, A.; KABIR, I. & JONES, P.K. - Patterns of morbidity and mortality
action, these drugs should be used in a controlled way in order to reduce                           in typhoid fever dependent on age and gender: review of 552 hospitalized patients
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